1. Field of the Invention
The present invention relates to an antireflective film, a polarizing plate using the antireflective film, and an image display device using the antireflective film or the polarizing plate on the outermost surface of the display.
2. Description of the Related Art
Antireflective films are generally provided on the outermost surface of the display for reducing reflectivity using the principle of optical interference, in order to prevent contrast reduction or reflection of an image due to the reflection of the outside light in image display devices such as a cathode ray tube displays (CRT), plasma displays (PDP), electroluminescence displays (ELD), and liquid crystal devices (LCD). For this, the antireflective film is required to have a high antifouling property against fat and oil components such as those from a fingerprint, a sebaceous oil, and the like, high physical strengths (scratch resistance, and the like), a high permeation rate, chemical resistance, and weather resistance (moisture/heat resistance, light resistance), in addition to high antireflective performances.
As a technology for providing an antifouling property, there has been generally known a method in which a silicone compound having a polydimethylsiloxane structure or a fluorine-based compound is used to reduce the surface free energy of a coated film surface. For example, there has been suggested that a compound having a long-chained fluorine-containing polyether chain and an unsaturated double bond in an antireflective film so as to provide an antifouling performance while not deteriorating the low refractive index and not reducing the rigidity could be used (Pamphlet of International Publication No. 03/022906). However, this compound does not necessarily satisfy the low refractive index property, the scratch resistance, and the antifouling durability, and therefore, there has been room for improvement.
Further, in the antireflective films as described above, at least a low refractive index layer which is a thin film layer having a thickness of 200 nm or less is provided on the outermost surface, and antireflection is performed by the optical interference of the low refractive index layer. However, in the case of a one-layer thin film interference type for performing antireflection on one layer of the low refractive index layers which have the simplest structure, there is no practical low refractive index material satisfying a reflectivity of 0.5% or less and further, having a neutral color tint, high scratch resistance, chemical resistance, and weather resistance. On the contrary, there have been known a multi-layer thin film interference type antireflective film for preventing the reflection by multi-layer optical interference, such as a two-layer thin film interference type for forming a high refractive index layer between a transparent support and a low refractive index layer, a three-layer thin film interference type for forming a medium refractive index layer and a high refractive index layer in this order between a transparent support and a low refractive index layer, and the like, so as to attain a reflectivity of 0.5% or less. In particular, the three-layer thin film interference type is preferred since it prevents the reflection at a wide wavelength range and gives a low reflectivity while inhibiting the reflected color.
In the case of a mono-layer, a layer having a lower refractive index than that of the substrate (low refractive index layer) may be formed to, in terms of optical layer thickness, a thickness of about ¼ of the designed wavelength. Furthermore, when further reduction of the reflection is required, it is known to form a layer having a refractive index higher than that of the substrate (high refractive index layer) between the substrate and the layer having a low refractive index (U.S. Pat. No. 3,034,044).
However, such a multilayer-type antireflective film can reduce the reflection, but a variation in the layer thickness or the refractive index of each of the layers leads to a change in the reflected colors. Particularly, if a fingerprint or a sebaceous oil is attached on the surface of a coated film, even if it is wiped off, some residue of the fat and oil components, if any, remains, and thus, are noticeable by the eyes because the attachment trace is more readily recognized as the change in the color tints, as compared to a mono-layer, from the change in the refractive index, and reduces the perceivability of the image. By this, in conventional multi-layer type antireflective films, even when the fluorine-containing compound having water/oil repellency or the silicone compound having a polydimethylsiloxane structure as above is used, the antifouling property could not be satisfied.